1. Field of the Invention
The present invention relates to a process for forming a deposition film. More particularly, it is concerned with such a process which is useful for forming a photoconductive film on a substrate by utilizing electric discharge including for example glow discharge.
2. Description of the Prior Art
Heretofore, for example, a photoconductive film composed of an amorphous material containing a silicon atom as the matrix is formed on a substrate by introducing a material for forming the film, in the gaseous state, into a deposition chamber which is reduced in the inside pressure, causing a glow discharge to take place and utilizing the plasma phenomenon. In this case, particularly when a photoconductive film having desired properties and a larger area is to be obtained, it is very difficult to increase the film forming speed while attempting to achieve uniformity in the film thickness, physical properties such as electrical, optical and photoelectrical properties and film quality over the whole area, as compared with the usual vacuum vapor deposition.
For example, a gaseous material such as SiH.sub.4, Si.sub.2 H.sub.6, SiF.sub.4, combination of SiH.sub.4 and SiF.sub.4, or the like is decomposed by using energy of electric discharge to form a film of amorphous silicon containing at least one of hydrogen atom and halogen atom (X), on a substrate. The amorphous silicon will be hereinafter called simply "a-Si(H,X)". When the electrical porperty of the film obtained by the above-mentioned method is to be utilized, in order to attain uniformity in the electrical property of the film over the whole area and improvement in the film quality over the whole area, it is necessary to decrease the film deposition rate and increase the temperature of the substrate since the electrical property of the film depends largely upon the film deposition rate and the substrate temperature, during formation of the film.
On the other hand, for the purpose of improving the producibility and mass-producibility, it is considered to increase the discharge power and flow amount of the gas to increase the film deposition rate. However, when the discharge power and/or flow amount of the gas are increased, the resulting film shows remarkable tendency to deteriorate in the electrical, optical and photoelectrical properties and increase dependence of the properties upon the area of the film. Therefore, in practice, it is very difficult to form a film of excellent quality. In order to realize the industrial application of preparing a photoconductive member having a photoconductive film composed of an amorphous material containing a silicon atom as the matrix, it is necessary to enhance the quality of film deeply related to the photosensitivity, repetition use characteristic and use environmental characteristic and improve the producibility and mass-producibility of the film as well as reproducibility while retaining uniform or even properties of the film.